Unoctseptium
Unoctseptium, Uos, is the temporary name for element 187. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 187 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Uos isotopes are theoretically possible between Uos 477 and Uos 819 (see "The Final Element", this wiki). Uos 477 through Uos 654 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Isotopes lighter than Uos 502 need more than twice the structural correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). Predicting whether or not the structure a nuclear drop can develop will allow it to survive for the 10^-14 sec required for it to bind an electron and so become an atomic nucleus is not usually possible at this time. Neutron shell closures have been predicted at N = 406 and 370(2),(3),(4). A shell closure has also been suggested at N = 318(5). The isotope Uos 593 requires 4 MeV of structural correction, which means some isotopes in the Uos 583 to Uos 598 band are likely. Uos 557 requires 9 MeV of structural correction energy, which means some isotopes in the band Uos 547 to Uos 562 may be possible if the closure is strong. Long beta-decay half-lives in this band are expected, so decay by alpha emission is likely. Uos 505 requires 25.5 MeV of structural correction energy, which implies that nuclides in this region are unlikely. Between Uos 502 and Uos 710 some drops may be nuclei. Outside this band, isotopes of Uos are nearly impossible. ATOMIC Electron structure of Uos has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Uos is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Uos to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Uos are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is probably impossible for lighter isotopes to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uos 583 to Uos 598 and Uos 547 to Uos 562 bands. Quantities amount to a few atoms per star at best. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 3. “Search for Superheavy Elements Among Fossil Fission Tracks in Zircon”; J. Maly & D.R. Walz; Stanford Linear Accelerator Center publication SLAC-PUB-2554; July 1980. 4. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-07-19)